Marc Andreessen

Andreessen is coauthor of Web browser Mosaic, cofounder of Netscape, founder of Opsware and cofounder of social network platform provider Ning. Now, with Opsware partner Ben Horowitz, he has started an investment firm, Andreessen Horowitz. Between the firm and his own holdings he has stakes in Twitter, Facebook, Groupon, LinkedIn, Skype and Zynga. Net worth: $600 million. Photographer: Ryan Anson/Bloomberg via Getty Images